Madame Wu, the fall of parity and the rise of the standard model

If you raise your right hand while looking in a mirror, the image in the mirror appears to have the left hand raised. This is an example of parity: the mirror image is equivalent to reality, but with left- and right-handed reversed. In 1956, an experiment by Chien-Shiung Wu at Columbia University showed that this equivalence does not hold in some nuclear decays: the universe is actually left-handed. This pivotal experiment began the journey to what we now know as the standard model of particle physics, the most successful fundamental theory of physics ever known.